Metal coating by vapor deposition



y 31, 1951 P. GODLEY, 2ND I 2,562,182

METAL COATING BY VAPOR DEPOSITION Filed Aug. 4, 1948 IN VEN TOR.

FIG.

ATTORNEY Phi/4o God/e 2 Patented July 31, i951 invention relates to the deposition on suitatmosphere and embracesimprovements both in 2,562,182 UNITE-b STAT-cs Pars ng 2,562,182 I METAL COATING BY VAPOR DEPOSITION,

Philip Godley, 2nd, Lexington, Mass, a'sslgnor't'o National Research Corporation, Cambridge, Mass., a corporation or Massachusetts- Application August 4, 1948, Serial No. 42,495

inethod and apparatus. The invention is par- -ticularly concerned with the deposition of metals on surfaces or supports containing occluded gases a'r other volatiles or substances which yield gases or yapors when heated.

"The invention is considered especially sig- 'niiicant as applied to the coating of cellophane fin-strip or 'sheetforin with aluminum and it will described with specific reference to that appucat'ion, it being understood that "the specific description will not be held limitativ'e. By means oi 'the invention 'analuminum coating can be applied to j'celloplian'e more evenly than heretofore audata substantially faster rate with fewer opeiational difficulties.

It has been previously recognized that mate- Y i'ials such as cellophane, and other plastic sheetsheeting formed of plasticized vinyl chlo-'- ride or vinyl acetate polymer or vinyl chloridevinyl acetate copolyme'r, for example, tend to fi bfihydrogen, water .vapor and possibly other gases" and vapors when contacted with a vaporized metal in a vacuum chamber, and that this gas and vapor evolution interferes with the coating operation by rendering it difiicultto maintain the vacuum. The hydrogen evolution .is especially pronounced in the case of cellophane where aluminum is employed as the coating metal, apparently due to reaction of the aluminum with hydroxyhcontaining compounds in the cellophane.

' Prior investigators have proposed that prior to the coating operation the surface to be coated be superficially preheated under reduced pressure, it being contended that when this is done, the necessary vacuum in the coating chamber can be maintained without 'difliculty. It is true that some improvement in results is achieved by so heating the support, but I have not 'found that the problem is thereby solved.

In accordance 'with my invention, I substantlall'y cool the support under reduced pressure subsequent to the preheating and before passing itto the coating zone. I have found that when this is done the gas and vapor evolutionis still further reduced and markedly so, particularly if the perheating is not limited to the surface to be coated but is extended to the body of the sup- In the most preferred form of the invenuse the support is also subjected to cooling influe'nces during the actual coating thereof.

My invention will be readily understood by refernce 'to the accompanying drawing illustrating schematically, in sectional elevation, a system ijtgpparatussuitable for its practice -when the support material instiip orwb'i'orm Dre:- ferred. the drawing. Fig. fldr'eprs'erits anest'ensiono'fFig. 1. v 'j I The apparatus, asuisaosea, will be seen' constituted of four compa'itiiients [0,1 l, l '2"aiii.'l l4, through which a strip Orwb to'becbalted, jiiicatedby the numera I5, is cbnseiutivlylpass'ed, the course of the 'Strip through thecol'il'paitiiiilt's being determined by lOllfS or idleis [6. 'Thistfip is is fed'from' a neuron n suitamysuppor d within compartment 1 lf0. compartment should be 'equil p'ed wi h" a pressure tig'htfiiooj'r .rcr whichjhin'ges 'l8"are'iindicatd. ,A' receivihg. 'roll l9 mounted in 'thefen'd compartment 14, which should also be provided with alpressuie tight 'for'which hinge elements are indicated, and may be driven in .the conventional. rotating drums 2| maintained in'fiictionaleiilgagement with the peri hery or the 1611.

Each of the compartments. l'll-ll'is maintamed under a suba'tmos'p heiic pressure, or conduits 22., 23. 21 and'25 being providedior this purpose. the material otthe strip .15 is .cellophaiieand that-the coating metal is aluminum, compartment 12 best maintained at a pressure notexcee'ding' 0.4 nucroiilof merecury, each of compartments ll and ['4 at a pressure of from 1 to v1D microns and compartment at a pressure o'ffrom 50 to 500 microns, it mechanical vacuum pump suflices in the case or compartment Ill and. a single difiusion pump'is usually sufiicient in the case .of compartments II and I4, but conduit -24, by .means of which compartment [2 isevacuated, should connect with a difiusion pump the action of which is supple.- mented by one or more booster pumps. 1

In compartment ID, the strip or web 15 Y passed over and under-heating elements, 16 which may be spaced and. supported as by insulating members 21. The heati ofv course, should not be of an intensity or io'ra duration causing severe embrittlement oflthe strip, but the strip should be. heated throughout in order thatvola? tiles will be removed from the b 'ody a s .we11, 1s from the surfaces thereof. Both the'intensityand duration of the heating are dependent 'onthe material of the strip and the limits'i'oranypar ticular material are easily determined by taxperimentation.

The strip is conveyed from compartmentill to compartment l I' through a slot in partition 2i therebetwe'en, the slot being covered-by a sealing element 29 which substantially prevents equal: izing of the pressures inthe compartments. Simi lar elements are secured over slots ipartlti'ons 3i and-32 constituting the sides of the-coating compartment. These elements may be formed-of natural or synthetic rubber or other suitable terial of a functionally equivalent nature. Where the material of thestrin-and the-coating operation are not adversel aifected thereby, mercury or other liquid seals may be substituted.

In compartment 1 I, the heated strip is cooled to reduce the vapor pressure of the volatiles not removed by the heating in compartment lo, the idlers or rollers l6 being so constructed as to enable the circulation of brine, a liquefied gas, or other suitable refrigerant therethrough. Alternatively, the strip may be passed over cooled metal plates, for example. Contact cooling is essential since the amount of air present is inadequate for cooling by convection. The extent of the cooling in the compartment is, of course, determined by the temperature at which the rollers are maintained and the residence period of the strip in the compartment. In general, the more thorough the cooling, the better the results. Thus, in the case of cellophane, every 10 C. drop in temperature reduces the vapor pressure of the contained volatiles 50%. It is my 'usual practice to lower the temperature of the strip during its residence in the cooling compartment at least 20 C.

From compartment I l, the strip is conveyed to compartment l2, the coating compartment, the strip being there passed under and in contact with a plate 33 preferably of metal, cooled as by coils 34 through which a suitable cooling agent is circulated. Below the plate is positioned a cup 35, shown as heated by a resistance coil 36, and shielded by an annular baflle 31. Cup 35 serves to evaporate the metal deposited on the surface of the strip presented for coating. Where it is desired to coat both surfaces or sides of the strip two cups may be used and certain obvious rearrangements made with respect to the course of the strip through the compartment.

Due to the cooling in compartment H, the volatiles not removed by the preheating remain substantially dormant, with the result that the necessary vacuum iseasily maintained in the coating compartment and the coating operation proceeds smoothly with even deposition of the metal.

The coated strip is conveyed through partition 32, constituting one of the walls of the coating compartment, through seal means as previously described and is wound on roll [9 in compartment (4. In some instances, it may be necessary or desirable to interpose a fifth compartment between compartments l2 and M. This fifth compartment may represent a spare or additional coating compartment, for example. An additional compartment or compartments may also be interposed between cooling compartment H and the coating compartment, it being advantageous at times to apply a preliminary nonmetallic coating before the metal coating is applied. Where possible, however, it is best to carry out the preliminary coating in the cooling compartment.

Exemplary of metals other than aluminum which may be employed in coating operations carried out in accordance with the invention may be mentioned: magnesium, silver, copper, gold, tin, zinc etc. Other supports or base materials in addition to those previously mentioned, which, like cellophane, tend to give oft water vapor and/or gases, include paper, textile fabrics, whether constituted of animal, vegetable or mineral fibers, e. g., silk, wool, cotton, rayon, asbestos cloth, fiber glass cloth, etc., artificial leather and the like.

The invention is not limited to the application of metal coatings, being highly useful in the coating of a support with a wax, for example.

I claim:

l. The process of vacuum deposition of a metal on a nonmetallic, flexible substrate which yields gases or vapors when heated, said process comprising the steps of passing said substrate through a heating zone evacuated to a pressure on the order of 50 to 500 microns Hg, heating both sides of said substrate during passage through said heating zone to drive from said substrate occluded gases and other volatiles resulting from said heating, said heating being of sufficient duration and intensity to remove volatiles from the body of said substrate as well as from the surface thereof, immediately thereafter moving said heated substrate from said heating zone to a cooling zone evacuated to a pressure lower than the pressure in said heating zone, providing a vapor barrier between said heating and cooling zones to prevent said evolved gases from entering said cooling zone and condensing on said substrate, cooling said substrate by at least 20 C. to prevent further evolution of gases from said substrate by passing said substrate in contact with at least one cooled surface in said cooling zone, said substrate being moved from said heating zone to said cooling zone and being contacted by said cooled surface prior to the time when the removal of volatiles is sufiicient to cause substantial embrittlement of said substrate, passing said cooled substrate from said cooling zone into a coating zone evacuated'to a pressure below about 0.5 microns Hg, vaporizing said metal in said coating zone, coating said substrate by condensing thereon said vapors of said metal, and shielding said substrate in said cooling zone from contact with metal vapors generated in said coating zone.

2. The process of vacuum deposition of a metal on a nonmetallic, flexible substrate which yields gases or vapors when heated, said process comprising the steps of passing said substrate through a heating zone evacuated to a pressure on the order of 50 to 500 microns Hg, heating both sides of said substrate during passage through said heating zone to drive from said substrate occluded gases and other volatiles resulting from said heating, said heating being accomplished at a plu-' rality of separate points as said substrate is advanced through said heating zone and being of sufiicient duration and intensity to remove volatiles from the body of said substrate as well as from the surface thereof, immediately thereafter moving said heated substrate from said heating zone to a cooling zone evacuated to a pressure lower than the pressure in said heating zone, providing a vapor barrier between said heating and cooling zones to prevent said evolved gases from entering said cooling zone and condensing on said substrate, cooling said substrate by at least 20 C. to prevent further evolution of gases from said substrate by passing said substrate in contact with a plurality of cooled surfaces in said cooling zone, said substrate being moved from said heating zone to said cooling zone and being contacted by said cooled surfaces prior to the time when the removal of volatiles is suflicient to cause substantial embrittlement or said substrate, passing said cooled substrate from said cooling zone into a coating zone evacuated to a pressure below about 0.5 microns Hg, vaporizing said metal in said coating zone, coating said substrate by condensing thereon said vapors of said metal, and shielding said substrate in said cooling zone from contact with metal vapors generated in said coating zone.

3. The process of vacuum deposition of a metal on a nonmetallic, flexible substrate which yields gases or vapors when heated, said process comprising the steps of passing said substrate through a heating zone evacuated to a pressure on the order of 50 to 500 microns Hg, heating both sides of said substrate during passage through said heating zone to drive from said substrate occluded gases and other volatiles resulting from said heating, said heating being of sufilcient duration and intensity to remove volatiles from the body of said substrate as well as from the surface thereof, immediately thereafter moving said heated substrate from said heating zone to a cooling zone evacuated to a pressure lower than the pressure in said heating zone, providing a vapor barrier between said heating and cooling zones to prevent said evolved gases from entering said cooling zone and condensing on said substrate, cooling said substrate by at least 20 C. to prevent further evolution of gases from said substrate by passing said substrate in contact with at least one cooled surface in said cooling zone, said substrate being moved from-said heating zone to said cooling zone and being contacted by said cooled surface prior to the time when the removal of volatiles is sufficient to cause substantial embrittlement of said substrate, passing said OOOled substrate from said cooling zone into a coating zone evacuated to a pressure below about 0.5 microns Hg, vaporizing said metal in said coating zone, coating said substrate by condensing thereon said vapors of said metal, shielding said substrate in said cooling zone from contact with metal vapors generated in said coating zone, and additionally cooling said substrate during condensation of said metal vapors thereon by maintaining said substrate in contact with a cooled surface during the time it is exposed to said metal vapors.

4. The process of claim 1 wherein said substrate comprises cellophane and said metal comprises aluminum.

PHILIP GODLEY, 2ND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,758,531 Pfanhauser May 13, 1930 2,074,281 Sommer Mar. 16, 1937 2,382,432 McManus et al. Aug. 14, 1945 2,402,269 Alexander et a1. June 18, 1946 FOREIGN PATENTS Number Country Date 306,902 Great Britain June 20, 1930 

1. THE PROCESS OF VACUUM DEPOSITION OF A METAL ON A NONMETALLIC, FLEXIBLE SUBSTRATE WHICH YIELDS GASES OR VAPORS WHEN HEATED, SAID PROCESS COMPRISING THE STEPS OF PASSING SAID SUBSTRATE THROUGH A HEATING ZONE EVACUATED TO A PRESSURE ON THE ORDER OF 50 TO 500 MICRONS HG, HEATING BOTH SIDES OF SAID SUBSTRATE DURING PASSAGE THROUGH SAID HEATING ZONE TO DRIVE FROM SAID SUBSTRATE OCCLUDED GASES AND OTHER VOLATILES RESULTING FROM SAID HEATING, SAID HEATING BEING OF SUFFICIENT DURATION AND INTENSITY TO REMOVE VOLATILES FROM THE BODY OF SAID SUBSTRATE AS WELL AS FROM THE SURFACE THEREOF, IMMEDIATELY THEREAFTER MOVING SAID HEATED SUBSTRATE FROM SAID HEATING ZONE TO A COOLING ZONE EVACUATED TO A PRESSURE LOWER THAN THE PRESSURE IN SAID HEATING ZONE, PROVIDING A VAPOR BARRIER BETWEEN SAID HEATING AND COOLING ZONES TO PREVENT SAID EVOLVED GASES FROM ENTERING SAID COOLING ZONE AND CONDENSING ON SAID SUBSTRATE, COOLING SAID SUBSTRATE BY AT LEAST 20* C. TO PREVENT FURTHER EVOLUTION OF GASES FROM SAID SUBSTRATE BY PASSING SAID SUBSTRATE IN CONTACT WITH AT LEAST ONE COOLED SURFACE IN SAID COOLING ZONE, SAID SUBSTRATE BEING MOVED FROM SAID HEATING ZONE TO SAID COOLING ZONE AND BEING CONTACTED BY SAID COOLED SURFACE PRIOR TO THE TIME WHEN THE REMOVAL OF VOLATILES IS SUFFICIENT TO CAUSE SUBSTANTIAL EMBRITTLEMENT OF SAID SUBSTRATE, PASSING SAID COOLED SUBSTRATE FROM SAID COOLING ZONE INTO A COATING ZONE EVACUATED TO A PRESSURE BELOW ABOUT 0.5 MICRONS HG, VAPORIZING SAID METAL IN SAID COATING ZONE, COATING SAID SUBSTRATE BY CONDENSING THEREON SAID VAPORS OF SAID METAL, AND SHIELDING SAID SUBSTRATE IN SAID COOLING ZONE FROM CONTACT WITH METAL VAPORS GENERATED IN SAID COATING ZONE. 